Worm Gear Flanged Butterfly Valve is used on firefighting apparatus and typically is used on larger lines, such as front and rear suction ports and tank to pump lines. A butterfly valve is also a type of flow control device, used to make a fluid start or stop flowing through a section of pipe. The valve is similar in operation to a ball valve. Rotating the handle turns the plate either parallel or perpendicular to the flow of water, shutting off the flow. It is a very well known and well used design.